Citigroup has 370 people in Frankfurt and could shift 200 more to Germany's financial centre from London to maintain access to the European single market after the UK leaves the European Union.

In January, UK Prime Minister Theresa May her Brexit plan in a speech signalling that Britain would leave the single market, which is a free trade bloc of European countries, in return for tougher immigration controls on EU citizens.

Financial firms in London will lose their ability to passport in to continental European clients from their UK base. Cowles said "it is the worst case and I think we have to adapt to it," in the interview with FAZ.

Cowles said that Citi was attracted by the "professionalism" the German regulator BaFin and would make a final decision by the middle of the year.

"We've reached out, we've talked to regulators and people at government across many countries in Europe, including Ireland, Italy, Spain, France, Germany and the Netherlands and we're in the process of evaluating each one of them," Cowles said.

Broker-dealers handle trades on behalf of clients such as funds or companies.

In the days after May's speech signalling her desire for a so-called hard Brexit, HSBC, JPMorgan, and UBS have all warned about job relocations.

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